WO2007116131A1

WO2007116131A1 - Device and method for capturing and eliminating agglomerated particles emanating from a motor vehicle particle filter

Info

Publication number: WO2007116131A1
Application number: PCT/FR2006/050334
Authority: WO
Inventors: Raphaël BOICHOT
Original assignee: Renault S.A.S
Priority date: 2006-04-11
Filing date: 2006-04-11
Publication date: 2007-10-18

Abstract

The invention relates to a device for capturing and eliminating agglomerated particles emanating from a particle agglomerator for the treatment of exhaust gases from a motor vehicle internal combustion engine, comprising an enclosure (29) having a wall which internally defines a duct (30) for the exhaust gases that is connected downstream to the particle agglomerator and upstream to an exhaust gas discharge pipe (C), an internal axial electrode (32) designed to create a radial electric field in the duct, and a set of annular plates (31) arranged transversely in the duct to arrest the agglomerator particles deflected by the electric field. The radially external peripheral edge of the annular plates (31) is spaced from the wall of the enclosure so as to form a space (41) which constitutes a passage for the stopped agglomerated particles or a storage volume.

Description

Device and method for capturing and removing agglomerated particles from a motor vehicle particle filter

The invention relates to the treatment of polluting components contained in a gaseous medium and, in particular, to the field of devices for filtering the exhaust gases of an internal combustion engine.

More particularly, the invention relates to a device for capturing and removing particles agglomerated by an electrostatic filtering device for particles contained in exhaust gases.

Indeed, the electrostatic type filtering devices generally use an electric field to cause an attraction of particles, also electrically charged, to a substrate on which the particles are fixed.

In this regard, reference may be made to the patent application WO 00/02549 which describes an electrostatic particle filtering device comprising a corona-type electrostatic filter comprising a cylindrical cage inside which the exhaust gases enter in order to of their filtering.

Reference can also be made to US Pat. No. 4,478,613, which describes another type of particle filtering device comprising an electrostatic filter and a mechanical particle separator.

The electrostatic filter comprises a tubular element having one of its closed ends and inside which there is a stack of disks concentric with respect to the axis of the tube. The tube is maintained at a zero potential while the discs are connected to a negative potential. The exhaust gases enter the tube through an opening and flow axially to exit through an opposite opening on the side. Discs carried at a negative potential constitute an emissive structure for generating an electric field between the inner surface of the tube and the discs. The exhaust gases pass through this field, the particles contained in the exhaust gas being electrically charged. The particles thus charged move radially under the effect of the electric field created to go to be deposited on the inner face of the tube where they accumulate in layers.

It is then necessary to remove the trapped particles.

This is generally achieved by using an agglomerated particle capture and removal device that recovers clusters of created particles that break off as soon as they reach a size sufficient for the friction forces exerted by the exhaust gases to pull them off. .

Thus, the invention proposes to improve the efficiency of existing devices for capturing and removing agglomerated particles.

The subject of the invention is therefore a device for capturing and eliminating agglomerated particles resulting from an exhaust gas treatment particle filter of an internal combustion engine of a motor vehicle comprising an enclosure comprising a wall defining on the inside. an exhaust gas duct connected upstream to a particle agglomerator and downstream to an exhaust gas discharge pipe, an inner axial electrode adapted to create a radial electric field in the duct and a set of plates annular arranged transversely in the conduit to stop agglomerated particles deflected by the electric field.

According to this device, the radially outer peripheral edge of the annular plates is spaced from the wall of the enclosure so as to form a space constituting a passage for stopped agglomerated particles or a storage volume.

According to a first embodiment of the invention, the annular plates are arranged in a perforated cylinder delimiting, with the wall of the capture and elimination device, said space.

For example, the perforated cylinder forms a grid. In another embodiment, said wall comprises at the location of the annular plates an area of enlarged internal diameter to delimit said space.

According to another advantageous embodiment, the annular plates are provided with a central passage coaxial with the wall, of dimensions able to avoid the appearance of pressure losses in the flow of the exhaust gas.

According to another characteristic of the invention, the device further comprises a heating electric resistance adapted to burn the particles arrested between the plates.

The invention also relates to a method for capturing and removing agglomerated particles from an exhaust gas treatment particle filter of a motor vehicle internal combustion engine by means of a capture device and agglomerated particle elimination as defined above, characterized in that it comprises the steps of:

recovery of the agglomerated particles at the outlet of the particulate filter by natural release of the clusters;

- Circulation of the agglomerated particles recovered in the conduit of the capture and disposal device;

- Deflection of the agglomerated particles to the annular plates under the effect of the electric field generated by the internal axial electrode; and trapping particles between and / or on the annular plates.

The particles trapped on the plates are then removed by heating or suctioning to an elimination device.

In one embodiment of this method, there is in fact a step of transferring the arrested particles to a space formed between the plates and the wall of the duct, and then sucking these particles to a particle removal system. .

Other objects, features and advantages of the invention will appear on reading the following description, given only by way of nonlimiting example, and with reference to the appended drawings in which:

- Figure 1 is a sectional view of an exhaust gas filtering system of an internal combustion engine incorporating a particulate filter and a device for capturing and removing agglomerated particles according to the invention;

FIG. 2 is a detailed view of the particle capture and removal device of the system of FIG. 1;

FIG. 3 is a curve illustrating the influence of the device according to the invention on the filtration efficiency of the system;

FIG. 4 illustrates another embodiment of the capture and elimination device according to the invention; and

FIG. 5 illustrates a third embodiment of the device according to the invention.

With reference to FIG. 1, an exhaust gas filtering system of an internal combustion engine will first be described.

This filtering system essentially comprises a particle filter 10 constituted by an electrostatic filtering cell ensuring entrapment and agglomeration of the particles carried by the exhaust gases, and a device 12 for capturing and removing agglomerated particles extracted from the filter cell 10 which opens into a pipe C of gas evacuation.

As can be seen in FIG. 1, the electrostatic filtering cell comprises an intake duct 2, a collector 4 and a filtering unit 3 located between the intake duct 2 and the collector 4.

The filter unit 3 comprises an external electrode 5 of generally cylindrical shape. This electrode 5 delimits internally an axial passage 6 for the gases which communicates at one of its ends with the pipe 2.

The outer electrode 5 has mutually opposite end surfaces 7 and 8. The front end surface 7 is axial contact with a ring 9 for fixing the external electrode 5 on the intake pipe 2. The ring 9 is connected to ground.

The external electrode 5 is open on the side of its front end surface 7, so that the central passage 6 communicates with the intake pipe 2.

The intake pipe 2 comprises an inlet orifice 13 on the opposite side to the outer electrode 5. A disk 14 abuts axially by a radial surface 15 against the end surface 8 of the external electrode 5 opposite to the intake pipe 2. The disk 14 axially closes the central passage 7 on the opposite side to the intake pipe 2.

The filter unit 3 comprises an external electrode 5 of generally cylindrical shape. The electrode 5 delimits internally an axial passage 6 for the gases which communicates at one of its ends with the pipe 2.

The filter unit 3 also comprises a central electrode 16 in the form of a rod 17 coaxial with the external electrode 5 and one end 18 of which is plugged into an insulating portion of the disc 14. The internal electrode 16 extends axially from its end 18 beyond the fixing ring 9 being bent to form a radial portion 19 radially out of the inlet pipe 2 through an opening 20. An insulator 21 is disposed in the opening 20 to electrically isolate the wall of the intake pipe 2 of the internal electrode 16. The radial portion 19 is electrically connected to a voltage source 22.

The collector 4 is disposed in a cylindrical envelope 23 which surrounds the external electrode 5. The cylindrical envelope 23 extends axially beyond the disc 14. It comprises an internal diameter greater than the external diameter of the external electrode 5, so that there is an empty annular space 24 between the cylindrical shell 23 and the external electrode 5. Finally, it communicates on the opposite side to the intake pipe 2 with a pipe 28 opening into the capture device 12 and removal of agglomerated particles. Indeed, in operation, the particulate-laden exhaust gases enter the intake pipe 2 through the inlet port 13. They flow into the central passage 6 of the external electrode 5, which communicates with the intake pipe 2, in which they are ionized and the electrically charged particles. As is conceivable, the end disc 14 prevents the axial passage of the exhaust gas. The exhaust gases are then deflected radially and pass through the external electrodes 5 which is gas permeable.

The external electrode 5 is maintained at a zero potential, the internal electrode 16 being brought to a positive or negative potential. The potential difference created between the external and internal electrode 5 induces the presence of an electric field in the axial passage 6. If this electric field has a sufficient intensity, in particular in the very near vicinity of the internal electrode 16, a partial or total ionization of the gases, or medium, occurs between the internal and external electrodes 16 and 5.

In the case of an internal electrode 18 brought to a negative potential, the particles present in the exhaust gases are mainly charged by collision and combination with free electrons. Given the low concentration of particles in the exhaust gas, the probability that an electron moving rapidly from the inner electrode 16 to the outer electrode 5 strikes a particle and combines with the latter is low. In order to properly charge the particles for electrostatic filtering, it is necessary to provide sufficient electronic avalanche. The internal electrode 16 must therefore be brought to a high potential, for example between 1 and 50 kV. The increase in the potential at which the internal electrode 16 is carried also has the effect of ionizing a gaseous medium in a larger volume. However, the ionization of the entire volume between the inner 18 and outer 5 electrodes requires considerable energy. In the case of an internal electrode 18 brought to a positive potential, the particles present in the exhaust gas pass through an ionized medium. There is a greater likelihood, in this case, that a particle encounters an ionized molecule and combines to form a positively charged particle. A positive internal electrode 16 allows an ionization of the volume between the internal electrode 16 and the external electrode 5 with a low energy input, being brought to a lower positive potential, for example between 1 kV and 50 kV.

The quasi-homogeneous electric field in the interelectrode space deflects the charged particles that migrate to the porous electrode. The electric field is heterogeneous only near the two electrodes. When the particles are in the vicinity of the porous electrode, of the order of 1 mm, the electric field lines converge towards the fibers of the porous electrode. The particles are then precipitated against the fibers by the large local increases in electric field. Since the electric field is zero inside the porous electrode and its developed surface is small, the majority of particles reaches the electrode from the first row of fibers and almost no depth capture takes place. The charged particles deposited on the inner face of the electrode agglomerate by electrostatic interactions and by Van der Waals forces. The particle clusters then grow to a size sufficient for the friction forces exerted by the exhaust gases tear them. The particle clusters grow to ejection out of the porous electrode in the form of agglomerates.

By way of example, the size ratio between the particles of the exhaust gases emitted by the engine and the particle clusters thus recovered is from 10 to 1000.

Referring more particularly to Figure 2, which illustrates on a larger scale the device 12 for capturing and removing agglomerated particles delivered by the particle filter 10, the device 12 essentially comprises a chamber 29 which defines internally a conduit 30 which receives the exhaust gas from the particle agglomerator 10. The enclosure 29 has a substantially cylindrical outer wall. It internally comprises a set of annular plates such as 31 extending transversely in the conduit 30 and evenly distributed along this conduit 30.

In addition, the capture device 12 comprises an internal axial electrode 32 which extends coaxially with the annular plates 31. This electrode 32 is intended to be connected to a voltage source, for example the same voltage source as that used for the As an example, the electrode 32 may also be in the physical continuity of the internal electrode 16.

It can be seen in FIG. 2 that the axial electrode 32 comprises, at its mutually opposite ends, radial portions 33 and 34 which pass through the wall of the enclosure 29, with the interposition of insulators 35 and 36 to be connected to the voltage source.

The device 12 may be completed by an annular heating resistor (not shown) which is for example fixed against the outer face of the upstream end annular plate, considering the circulation of the exhaust gas. This heating resistor is connected to a voltage source, low voltage.

Thus, thanks to this arrangement, the agglomerated particles conveyed by the exhaust gases, and which are electrically charged, are deflected by the central electrode 32 towards the annular plates 31 to be stopped there. Indeed, these plates then constitute, for particle clusters, abutments they come crashing during their movement. They are then trapped by the space delimited by the adjacent plates.

The annular heating resistor when activated then causes a rise in temperature of the particles sufficient to cause their combustion. This combustion can then propagate along the chamber 29 thanks to the presence of axial and coaxial orifices which are formed in the plates 31. Note that the plates are spaced from the wall of the chamber 29. Indeed, at the location of the plates 31, the wall of the chamber 29 has a zone 40 of increased diameter. The space between the outer peripheral edge of the plates and the wall of the chamber 29 forms a volume 41 for storing the particles. Thus, the outer peripheral edge of the annular plates 31 and spaced from the inner face of the peripheral wall of the chamber 29 so that the particles stopped by the plates 31 are transferred to the volume 41 by suction. Such a volume may also constitute a passage for the evacuation of particle clusters to a post-treatment device.

It will be chosen either to suck the particles contained in the volume 41 to drive them to a destruction device, or to destroy them in situ on the collection plates by resistive heating.

It can be seen in FIG. 2 that the wall of the enclosure 29 opens into a passage 43 which makes it possible to put the device 10 in communication with an external device for destroying the soot.

It will be noted that the plates 31 are advantageously arranged in a perforated cylinder 42 that is generally cylindrical and extends coaxially in the chamber 29 against which the plates 31 rest. Preferably, the perforated cylinder 42 is in the form of a cylindrical grid whose meshes have a size sufficient to let the agglomerated particles.

Referring now to FIG. 3, which shows the evolution of the filtration efficiency of the particle filter as a function of the feed current I of the central electrode 16, respectively using a capture device and removal of the agglomerated particles (curve A) and in the absence of such a device (curve B), it is found that the presence of the device 12 can significantly improve the efficiency of the particulate filter 10.

Note however that the invention is not limited to the embodiment described. Indeed, as shown in Figure 4, the perforated cylinder 42 is optional so that the passages delimited between two adjacent plates 31 can directly lead into the volume 41.

In addition, as can be seen in FIG. 5, according to another embodiment, the annular plates 31 have a central passage 44 of enlarged diameter to substantially correspond to the diameter of the end zones 45 and 46 of the chamber 29 of so that the plates are offset from the flow so as not to cause a pressure drop therein.

Finally, it should be noted that in the various embodiments, the annular plates 31 are mounted on a threaded rod 47 in order to allow precise positioning of the plates in the chamber 29.

The electrode 16 and the electrode 31 can advantageously be connected to the same potential and fed by the same high voltage device.

Claims

1. Apparatus for capturing and removing agglomerated particles from an exhaust gas treatment particle filter of an internal combustion engine of a motor vehicle, comprising an enclosure (29) having a wall internally defining a duct (30) for the exhaust gas connected upstream to a particle agglomerator and downstream to an exhaust gas pipe (C), an inner axial electrode (32) adapted to create a radial electric field in the duct and a set of annular plates (31) arranged transversely in the duct to stop the agglomerated particles deviated by the electric field, characterized in that the radially outer circumferential edge of the annular plates is spaced from the wall of the enclosure so as to forming a space (41) constituting a passage for the stopped agglomerated particles or a storage volume.

2. Device according to claim 1, characterized in that the annular plates are arranged in a perforated cylinder (12) defining, with the wall of the capture and elimination device, said space.

3. Device according to claim 2, characterized in that the perforated cylinder (42) forms a grid.

4. Device according to claim 1, characterized in that the wall of the enclosure comprises at the location of the annular plates an area (40) of enlarged inner diameter to define said space.

5. Device according to any one of claims 1 to 4, characterized in that the annular plates are provided with a passage (30) central coaxial with the wall, of dimensions capable of preventing the occurrence of pressure losses in the exhaust gas flow.

6. Device according to any one of claims 1 to 5, characterized in that it further comprises a heating electric resistance adapted to burn the particles arrested between the plates.

7. A method for capturing and removing agglomerated particles from an exhaust gas treatment particle filter of a motor vehicle internal combustion engine by means of a device for capturing and removing particles agglomerates according to any one of claims 1 to 6, comprising the following steps:

recovering agglomerated particles at the outlet of the particulate filter (10);

- circulating agglomerated particles recovered in the conduit (30) of the capture and disposal device;

deflecting the agglomerated particles towards the annular plates (31) under the effect of the electric field generated by the internal axial electrode; and

trapping particles between and / or on the annular plates.

8. The method of claim 7, characterized in that it further comprises a step of transferring the arrested particles to a space formed between the plates and the duct wall, and then suction of these particles to a disposal system. of particles.